1. Field of the Invention
The present invention relates to an injection molding machine, and more particularly to an injection molding machine designed to prevent a stationary platen from inclining due to a nozzle touch force from an injection unit.
2. Description of the Related Art
FIGS. 6a, 6b and 7 are diagrams illustrating the conventional injection molding machine, and specifically a mold clamping mechanism thereof. FIG. 6a shows a front view of the injection molding machine, FIG. 6b shows a view from the right side as seen from the front in FIG. 6a, and FIG. 7 shows a perspective view.
A conventional mold clamping mechanism of the injection molding machine comprises a stationary platen 20 fixedly mounted along its bottom edge on a base 1 of the injection molding machine, a rear platen 40 set on the base 1 by rear platen support members 9, a plurality of (four) tie bars connecting the stationary platen 20 and the rear platen 40, a movable platen 30 set on the base 1 by a movable platen support member 8, and a drive mechanism, not shown, that moves the movable platen 30.
A stationary-side mold, not shown, is mounted on the stationary platen 20, a movable-side mold, not shown, is mounted on the movable platen 30, and the movable platen 30 is moved toward the stationary platen 20 by the drive mechanism to close the mold and then clamp it. In addition, an injection unit is disposed on the side of the stationary platen 20 away from the movable platen 30, the injection unit is advanced and a nozzle at the front of a screw cylinder 6 is pressed against a sprue bushing on the fixed-side mold, a nozzle touch force is applied, an injection screw is advanced and melted resin is injected into the clamped mold. It should be noted that, in FIGS. 6a, 6b and 7, reference numeral 7 indicates a nozzle touch drive shaft that advances the injection unit and touches the nozzle at the front of the screw cylinder 6 against the fixed mold.
The stationary platen 20 is fixedly mounted all along one edge (its bottom edge) on the base 1, against a central portion of which the nozzle touch from the screw cylinder 6 is applied. If, as shown in FIG. 6a, a height (length) from the bottom edge of the stationary platen 20 (where the stationary platen 20 is continuously fixedly mounted on the base 1) to the point at which the nozzle touch force acts is L1, and the nozzle touch force from the screw cylinder 6 is F, then a moment L1×F is applied to the stationary platen 20, which tends to cause the stationary platen 2 to tilt toward the movable platen 30 and incline. Consequently, to prevent this inclination a variety of countermeasures have been proposed.
Known stationary platen inclination countermeasures include providing a rib on the lower part of the nozzle touch side of the stationary platen and connecting a support provided on the base with the rib to prevent the stationary platen from inclining (JP 2000-289069A); providing extensions that project toward the injection unit side from both ends of the bottom of the stationary platen and fixedly mounting the extensions on the base to prevent the stationary platen from inclining (JP 2003-25378A); and providing multiple (two) nozzle drive units arranged symmetrically around the central axis of the injection nozzle and composed of rod-shaped moving screws, tubular fixed shafts the base end parts of which are fixed to a stationary platen, and fixing nuts combined with the screws, with the screws rotated to advance the injection nozzle against the stationary platen as the nozzle touch force is balanced to prevent inclination of the stationary platen (JP 09-234765A).